1. Field of the Invention
My invention relates to freezer enclosures which are positioned on grade or on soil and to refrigeration systems cooling such freezers and to means for improving the thermodynamic efficiency of such refrigeration systems while preventing freezing of the soil under the freezer enclosure.
2. Background
Frost Heaving, Cause:
When freezers are located on grade, there is heat flow from the ground on which the insulated floor of the freezer rests through the insulated floor to the freezer. Consequently the ground under the freezer floor tends to drop in temperature and eventually approach the temperature inside the freezer itself. As the ground under the freezer floor cools, the vapor pressure of water or moisture within the cooled ground drops. This reduction in water vapor pressure within the cooled ground under the freezer establishes a vapor pressure differential favoring water vapor flow from the warmer moisture residing elsewhere in the ground, and possibly from the moist air surrounding the freezer above grade, to the cooled earth under the freezer. There the moisture attracted by the cooler ground under the freezer condenses and eventually freezes.
Over a period of time, temperature changes within the freezer and seasonal changes of ground temperature, causes thawing and refreezing of the moisture that has been attracted to and now resides within the earth under the freezer. Eventually the freeze/thaw cycles cause expansion of the ice formed in the earth under the freezer to the extend that the freezer floor is bulged upward and is disrupted. This bulging of the freezer floor is called frost heaving.
Frost Heaving, Prevention, Prior Art;
While repair of a heaved floor by heating the bulged portion and area surrounding is sometimes effective to reduce the bulge, the floor is always damaged and subject to repeat heaving. Therefore the most effective long term remedy is removal and rebuilding of bulged floor with heat. Consequently, since it has long been known that frost heaving of unheated freezer floors erected on grade is likely to occur, conservative construction practice has required that means for heating the ground immediately underneath on-grade freezers be provided. In fact, the following statement appears at page 5 of chapter 24 "Refrigerated Warehouse Design" of the 1994 ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) Refrigeration Handbook under the heading "Floor Construction"
Refrigerated facilities held above freezing need no special under-floor treatment. A below-the-floor vapor barrier is needed in facilities held below freezing, however. In these facilities, the sub-soil eventually freezes, and any moisture in this soil will also freeze and cause floor frost heaving. In moderate climates, underfloor tubes vented to ambient air are sufficient to prevent heaving. Artificial heating, either by air circulated by underfloor ducts or glycol circulated through plastic pipe is the preferred method to prevent frost heaving. Electric heating cables installed under the floor can also be used to prevent frost formation. The choice of heating method depends on energy cost, reliability, and maintenance requirements.
"Further, in the same chapter at page 10 under the heading Floors", the following appears referring to circulation of a warmed liquid under the freezer.
"The pipe grid system . . . is usually best . . . A source of heat for this system can be obtained by a heat exchanger in the refrigeration system, steam or gas engine exhaust. The temperature of the recirculated fluid is controlled at 50 F. to 70 F., depending on design requirements. Almost universally the pipes are made of plastic.
The pipe grid system is usually placed in the concrete slab directly under the insulation . . . The fluid should be an antifreeze solution such as glycol with the proper inhibitor.
All known experiences related to the use of a heat exchanger in the refrigeration system to provide heat to the glycol stream place the heat exchanger either in series with the condenser at its hot gas inlet or in parallel in the condenser. Nowhere in the Handbook or elsewhere in the literature could there be found any reference to the potential usefulness of the cooling effect of the glycol solution, which had been employed for warming the freezer floor, for cooling or sub-cooling liquid refrigerant flowing to the expansion device.